System for borehole depth and tool position measurements

ABSTRACT

Disclosed is a method and system for monitoring the depth of a borehole and the distance between the drilling tool and the bottom of the borehole which is usable concurrently with the drilling of the borehole. A rotary pulse generator is provided driven by the slow sheave of the crown block which senses upward and downward movement of the drill string and which provides a pair of pulse train signals representing movement through incremental length segments of predetermined magnitude such as, for example, 1 foot. A discriminator is provided for discriminating between the upward and the downward pulses and for providing a pair of pulse train signals the first representing downward movement and the second representing upward movement, of the drilling tool. The pulses of the first signal are summed by a first pulse counter which in turn provides an output signal representing the accumulated depth of the borehole. A second pulse counter is provided for summing the pulses of the second signal and for subtracting from the resulting sum the pulses of the first signal and for providing a second output signal corresponding to the distance between the drilling tool and the bottom of the borehole. Inhibit means are provided for inhibiting the summing performed by the first counter when the aforementioned second output signal is greater than zero and for inhibiting the subtracting performed by the second counter when the second output signal is not greater than zero. Also, means are provided for inhibiting the operation of both counters when the weight of the drill string is off the drilling cable.

[ 1 Feb. 22, 1972 SYSTEM FOR BOREHOLE DEPTH AND TOOL POSITION MEASUREMENTS Primary ExaminerRichard C. Queisser Assistant ExaminerMarvin Smollar Altomey-K. E. Kavanagh, Thomas H. Whaley and Robert J. Sanders, Jr.

[ ABSTRACT Disclosed is a method and system for monitoring the depth of a borehole and the distance between the drilling tool and the bottom of the borehole which is usable concurrently with the drilling of the borehole. A rotary pulse generator is provided driven by the slow sheave of the crown block which senses upward and downward movement of the drill string and which provides a pair of pulse train signals representing movement through incremental length segments of predetermined magnitude such as, for example, 1 foot. A discriminator is provided for discriminating between the upward and the downward pulses and for providing a pair of pulse train signals the first representing downward movement and the second representing upward movement, of the drilling tool. The pulses of the first signal are summed by a first pulse counter which in turn provides an output signal representing the accumulated depth of the borehole. A second pulse counter is provided for summing the pulses of the second signal and for subtracting from the resulting sum the pulses of the first signal and for providing a second output signal corresponding to the distance between the drilling tool and the bottom of the borehole. Inhibit means are provided for inhibiting the summing performed by the first counter when the aforementioned second output signal is greater than zero and for inhibiting the subtracting performed by the second counter when the second output signal is not greater than zero. Also, means are provided for inhibiting the operation of both counters when the weight of the drill string is off the drilling cable.

1 Claims, 5 Drawing Figures 3 4mm... [AM/e,-

first? Fans/are ElElElElEl aze UUUDU PATENIEDFEB 2 2 I972 OOOOO DEBUG 00000 UDDUU SHEET 1 [1P2 SYSTEM FOR BOREHOLE DEPTH AND TOOL POSITION MEASUREMENTS BACKGROUND OF THE INVENTION This invention relates to borehole depth measurements and more particularly relates to a method and system for continuously monitoring the depth of a borehole and the distance the drilling tool is raised from the bottom of the borehole substantially concurrent with the drilling of the borehole.

in drilling for petroleum and other mineral deposits it has been practice to monitor the depth of the borehole by maintaining a count of the sections of drill pipe of the drill string as they are added. Also, when casing is added to the borehole it has been practice to verify the count by counting the sections of drill pipe as they are removed, and by initially noting the distance below the surface of the uppermost section of drill pipe the borehole depth can be determined. However, this method is time consuming and when the new drill string is established the accumulated error of the sum of the lengths of the drill pipe sections of the new drill string can be sufficiently great to cause a substantial uncertainty of the position of the drilling tool as it nears the bottom of the borehole. As a consequence, the new drill string when completed is lowered very slowly to prevent any damage thereof arising from the possibility of impact of the drilling tool with the bottom of the borehole. These procedures are time consuming in the absence of a system for automatically indicating the exact position of the drilling tool with respect to the bottom of the borehole.

Furthermore, there is increased interest regarding computer monitoring of the borehole drilling procedure. The invention as herein disclosed is directed to the solution of the aforementioned problems wherein there is provided a method and a system for automatically monitoring the depth of a borehole and the distance between the drilling tool and the bottom ofa borehole substantially concurrent with the drilling thereof and which lead to signals of this information which are amenable to being monitored by digital computer.

SUMMARY Briefly stated, one aspect of the invention resides in a system for providing continuous information of the depth ofa borehole and of the distance between the borehole drilling tool and the bottom of the borehole. The information is provided in the form of first and second output signals respectively representing the aforementioned measures. The system of the invention is used in conjunction with a conventional borehole drilling facility including a drilling structure, a drill string coupled with the drilling tool, means for rotating the drill string, support means such as a traveling block and a drilling cable for supporting the drill string, a crown block mounted in the drilling structure having at least one rotatable sheave, the drilling cable engaging the sheave and the traveling block, and means coupled with the drilling cable for raising and lowering the drill string and drilling tool. As the drill string is raised or lowered in the borehole, its movement along the path of the borehole is manifested by movement of the drilling cable which is in turn manifested by a corresponding rotation of the rotatable sheave. The system of the invention comprises: signal generating means coupled with the rotatable sheave for generating an incremental depth first signal representative of incremental length segments of predetermined magnitude through which the drill string descends in the borehole and for generating an incremental height second signal representative of the incremental length segments of the same predetermined magnitude through which the drill string is raised in the borehole. Also, included are first summing means coupled with the signal generating means for summing the quantity of segments represented by the first signal and for providing a first output signal representative of the sum of the incremental depth length segments, the first output signal accordingly representing the accumulated depth of the borehole. The system further includes second summing means coupled with the signal generating means for summing the quantity of segments represented by the incremental height second signal for subtracting from the resulting sum the quantity of segments represented by the incremental depth first signal and for providing a second output signal representative of the resulting difference. The system of the invention further includes inhibit means coupled with the first and second summing means for inhibiting the summing performed by the first summing means when the second output signal of the second summing means is greater than zero and for inhibiting the subtracting performed by the second summing .means when the second output signal is not greater than zero. Accordingly, the first output signal indicates the depth of the borehole starting with zero at the earths surface and increasing as the borehole is drilled. When the drilling tool is raised from the bottom of the borehole the second output signal ,indicates the distance between the drilling tool and the bottom of the borehole while the first output signal continues to indicate the accumulated depth of the borehole. When the drilling tool is lowered from the latter position the second output signal continuously indicates the distance between the drilling tool and the bottom of the borehole while the aforementioned first summing is inhibited to maintain unchanged the first output signal representing the accumulated depth of the borehole. The first output signal remains unchanged until the second output signal returns to zero, This occurs when the drilling tool is returned to the bottom of the borehole. Accordingly, the first output signal always indicated the accumulated depth of the borehole and the second output signal always indicates the distance between the drilling tool and the bottom of the borehole.

In a further embodiment of the invention the aforementioned system is enlarged to prevent erroneous indications during the addition of lengths of drill pipe to the drill string as the borehole is deepened. Weight sensing means are provided coupled with the first support means for sensing the weight of the drill string supported by the drilling structure. The weight sensing means are adapted to inhibit the summing and subtracting performed by the first and second summing means when the weight supported by the support means is below a predetermined set-point value. The set-point value exclusive of the weight of the first support means, i.e., the traveling block and associated equipment, is set at a value less than the portion of the total drill string weight supported by the drilling structure, i.e., the difference between the total drill string weight and the net load on the drilling tool. The set-point is also at a value greater than the weight of the additional length of drill pipe to be hoisted and added to the drill string. Accordingly, when the weight of the drill string is removed from the traveling block and the drilling cable, any incremental depth and height signals generated as a consequence of the movement of the drilling cable while adding additional sections of drill pipe are added are prevented from influencing the first and second output signals.

Another aspect of the invention resides in a method for providing the aforementioned first and second output signals. This method includes the steps of generating an incremental depth first signal in the form of a first pulse train as the drilling tool descends, each pulse of the first signal corresponding to downward movement of the drilling tool through an incremental length segment of predetermined magnitude, generating an incremental height second signal in the form of a second pulse train as the drilling tool is raised in the borehole. Each pulse of the second signal corresponding to upward movement of the drilling tool through a length segment of the aforementioned magnitude, and, summing the quantity of the pulses of the first signal and providing a first output signal corresponding to the resulting sum. Accordingly, the first output signal corresponds to the accumulated depth of the borehole in multiples of the predetermined incremental length segments. The method of the invention further includes the steps of summing the quantity of the pulses of the second signal from the resulting sum subtracting the quantity of the pulses of the first signal generated as the drilling tool is lowered in the borehole, providing a second output signal corresponding to the resulting difference, inhibiting the first mentioned summing step when the second output signal is greater than zero, and inhibiting the aforementioned subtracting step when the second output signal is not greater than zero. Accordingly, the first output signal always indicates the accumulated depth of the borehole and the second output signal indicates the distance between the drilling tool and the bottom of the borehole when the drilling tool is raised therefrom.

An important feature of the system of the invention is obtained by mounting the signal generating means to engage the aforementioned crown block sheave the use of a secondary cable coupled to the traveling block for registering and conveying its movement to the signal generating means is avoided. Another advantage is obtained by use of aforementioned weight sensing means to inhibit operation of the system when drill pipe or casing are added. In this way, manual switching on and off of the system is avoided during these operation. Yet another advantageous feature of the system can be realized by mounting the signal generating means to engage the slow sheave of the crown block, that is, the sheave adjacent to the motionless sheave. The slow sheave always experiences the same degree of motion relative to the drill string regardless of the number of sheaves utilized in the crown block. In this way the system is usable-without requiring speed ratio adjustment of the signal generating means when the number of crown block sheaves are varied, resulting in great flexibility of use.

In view of the foregoing it is an object of the invention to provide an improved system and method for monitoring the depth of a borehole and the distance between the drilling tool and the bottom of the borehole.

Another object of the invention is to provide an improved method and system for continuously monitoring while drilling the depth of a borehole and the distance between the drilling tool and the bottom of the borehole, the successful results of which are unaffected by procedures for adding sections of drilling pipe to the drill string as the borehole is deepened.

Another object of the invention is to provide an improved method and system for continuously monitoring the depth ofa borehole and the distance between the drilling tool and the bottom of the borehole the successful results of which are unaffected by procedures for addition of casing to the borehole.

Another object of the invention is to provide an improved method and system for continuously monitoring the depth ofa borehole and the distance between the drilling tool and the bottom of the borehole of improved flexibility which does not require the use of a separate drive system coupled with the traveling block, or its associated equipment, and which is interchangeably usable with crown blocks having any number of sheaves.

Another object of the invention is to provide a method and system usable in conjunction with the drilling procedures of a borehole for generating signals representative of the depth of the borehole and of the distance between the drilling tool and the bottom of the borehole; the signals being amenable to monitoring and use thereof by a computer.

These and other objects, advantages and features of the invention, will be more fully understood by referring to the following description and claims, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view, in simplified form, ofa borehole drilling facility.

FIG. 2 is an elevation view of the upper portion of the drilling structure of FIG. 1 showing the pulse signal generator of the system of the invention engaging a sheave of the crown block, and illustrating in block diagram form, other components of the system of the invention.

FIG. 3 is a cross-sectional view of FIG. 2 taken along the plane 3-3.

FIG. 4 is an isometric view showing details of the mounting provisions for the pulse signal generator as mounted in FIG. 2.

FIG. 5 is a cross-sectional view, taken through the axis of rotation of the pulse signal generator, illustrating its coupling with the friction driven wheel of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 there is shown in simplified form a drilling structure 10, including a conventional crown block 1 I, mounted in the upper portion of the structure, a drilling cable 12, and a traveling block 13 suspended from the crown block overhead by the drilling cable. The crown block 11, and the traveling block 13, each include a plurality of sheaves over which passes the drilling cable for obtaining the desired mechanical advantage for raising and lowering the traveling block in the conventional way. The traveling block 13 includes a conventional hook 14, from which is suspended a swivel 15 from which, in turn, is suspended a drill string 16. The drill string 16 includes a kelly 17 the upper portion of which is connected with the swivel 15. The drill string further includes drill pipe 18 and a drilling tool 19 conventionally connected to the lower end thereof. The kelly I7 passes through a rotary 20 which is coupled with a suitable source of rotational power, not shown, for rotating the drill string to drill the borehole. The stationary end of the drilling cable is anchored to the platform of the structure with a conventional cable anchor 25, which includes a conventional force transducer for sensing the tension in the drilling cable at its anchor point. This tension is proportional to the portion of the drill string weight which is supported by the drilling cable; the balance of the drill string weight is conventionally applied as a downward force by the drilling tool on the earth formation during drilling. The portion ofthe drill string weight supported is controlled by the draw works, not shown, which applies tension to the free end of the drilling cable 12 as it passes beneath a sheave 26. From its anchor point 25, the drilling cable extends upwardly passing over a first sheave 27 of the crown block 11. This sheave remains stationary as the drilling cable is drawn by the draw works. From the first sheave the drilling cable makes several passes engaging the moving sheaves of the crown block, and the traveling block thereby gaining mechanical advantage and passes from the last, or high-speed sheave of the crown block, downward to the draw works. The second sheave 28, of the crown block, commonly referred to as the slow sheave, experiences 2 lineal feet of movement along its periphery for each foot of linear movement of the drill string regardless of the number of crown block and traveling block sheave pairs used.

Referring now to FIG. 2 which illustrates in greater detail the region of the crown block which is of interest, the first and second sheaves, 27 and 28, are illustrated mounted to the left portion of the crown block. Engaging the slow sheave 28 is a friction driven wheel 30 which is made of a hard resilient material such as hard rubber. The wheel 30 is mounted beneath the slow sheave in a position such that the drilling cable 12 which passes over the sheave clears the friction driven wheel 30 and its mounting provisions. The axis of rotation of the wheel 30 is parallel to the axis of the sheave 28 and the wheel 30 engages the slow sheave by contacting the root region of the semicircular cable groove of the sheave. The outer shape of the wheel 30 is essentially that of thin disclike circular cylinder having its two peripheral corners chamfered and a cylindrical flat portion between the chamfers. The chamfers are arranged such that each makes an angle of about 30 with the cylindrical portion of the wheel and the thickness of the wheel is about one-half inch. The depth of the chamfers along the fiat face of the wheel is about one-sixteenth inch, therefore leaving about three-eighths inch of cylindrical portion along the perimeter of the wheel between the chamfers. This configuration is preferred for use in conjection with a sheave having a cable groove of 94-inch root radius, which is commonly used in conjunction with l /z-inch diameter drilling cables. ln the aforementioned configuration the wheel engages the sheave with its chamfers contacting the cable groove in a nearly tangential manner. As a consequence there is a mild wedging action in the cable groove resulting in a positive friction drive of the wheel 30. It is to be appreciated by those skilled in the art that a positive drive free of slippage is of great importance so that erroneous indications of the borehole depth are avoided. Also, a hard wheel is preferred to enhance its life and its repeatability. Accordingly, it is preferred that the circumferential portion of the driven wheel be made of a hard resilient material such as rubber having a hardness in range of about 90 to 100 durometer.

A mounting bracket 31 is provided to which is rotatably mounted the driven wheel 30 and which is fitted with a spring 54 for urging the wheel into engagement with the sheave with an engagement force of about 40 pounds. The mounting bracket 31 is in turn clamped to an l-beam 32 of the crown block frame by a pair of bolts 33. Clamping in this way is preferred to avoid weakening of the crown block frame should other methods of fastening be used such as welding or by bolts passing through holes in the crown block frame.

Mounted to the mounting bracket 31 is a rotary pulse generator 35 having its input shaft coupled to the driven wheel 30. The pulse generator 35 is a conventional bidirectional rotary pulse generator of the electrical-optical type, for converting rotary motion to digital information by generating two electrical; pulse train signals whose phased relationship is determined by the direction of rotation of its input shaft, and the occurrence of each of the pulses designates rotational movement of its input shaft through a predetermined angle. The coupling of the pulse generator 35, to the driven wheel 30, can be either direct as illustrated, and as is preferred, or it can be bypassing through a gear box for either reducing or multiplying the speed of the driven wheel depending upon the desired frequency of the pulse train. A direct drive is preferred when a driven wheel of about 7 inches in diameter is used in conjunction with a slow sheave of about 60 inches in diameter.

The two pulse train signals from the pulse generator 35 are carried by suitable electrical wiring to a pressure switch 40. The pressure switch is hydraulically coupled to a conventional force transducer 41 which is conventionally mounted at the drilling cable anchor 25 for sensing the cable tension at the anchor point. The force transducer 41 provides a hydraulic pressure signal proportional to the aforementioned tension which is carried to the pressure switch 40, by a conduit 42. The pressure switch 40 is calibrated to open its contacts when the pressure in the conduit 42 drops below a predetermined set-point value which is indicative of a release of the drill string weight from the traveling block 13. The contacts are in turn wired to receive and pass the pulse train signals from the pulse generator and to interrupt passage of these signals when the sensed pressure drops below the predetermined set-point value.

The pulse train signals pass from the pressure switch 40 to a conventional discriminator 43. At the input of the discriminator both pulse train signals are present regardless of the direction of rotation of the shaft of the pulse generator 35. However, when this rotation is in one direction such as corresponding to downward movement of the drill string, the first of the pulse train signals, which is essentially a square wave pulse train, leads the second by a phase angle of about 90. When the direction of rotation is reversed, the second pulse train signal leads the first by the same phase angle. The discriminator 43 senses this phase angle and provides an output pulse train signal through either of two output circuits depending upon the direction of rotation of the pulse generator shaft. The first output circuit of the discriminator 43 carries the down" signal to a relay 44. The second output circuit carries up" signal to a conventional bidirectional digital pulse counter 45. The counter 45 is adapted to count the pulses of its input signal and provide an output signal in the form of a digital display corresponding to the sum of the quantity of these pulses. This display signal corresponds to the distance the borehole drilling tool is raised from the bottom of the borehole.

When the relay 44 is energized to a first operative state it latches and permits the down pulse train signal to pass through its contacts to a first output circuit of the relay and thence to a conventional digital pulse counter 46. The counter 46 is adapted to count the pulses of the down signal and provides a visual display output signal corresponding to this count. Accordingly, the output display of the counter 46 corresponds to the accumulated depth of the borehole. The counters 45 and 46 include conventional presetting provisions so that they can be preset to any preselected reading upon commencement of drilling the borehole. Also, with respect to the counter 45 this feature is useful during the casing operations discussed hereinafter.

The relay 44 is a two coil latching relay which latches over and remains in either one of its two operative states depending upon which of its two coils is energized. In its first state it permits the down pulse train to pass to the counter 46. In its second state it opens this circuit and permits the down" pulse train to pass to its second output circuit which is connected with the counter 45. A relay driving amplifier 47 is provided for powering the coils of the relay 44.

When the borehole is started both counters are manually preset to zero. The counter 45 is adapted to provide a signal when it has a zero reading. This signal is carried to the relay driving amplifier which includes appropriate circuitry such as transistor switching and an output electrical circuit to energize the relay 44, causing it to latch into its first state. In this state the down pulse train is permitted to pass to the counter 46 as the borehole is deepened, and this counter displays the borehole depth. When the drilling tool is raised from the bottom of the borehole the discriminator 43 passes the up" pulse train to the counter 45. Wired in parallel with the counter, with respect to this signal, is the relay driving amplifier 47, which is adapted to energize the relay 44 to its second operative state upon the occurrence ofthe up signal.

The up pulses are summed by the counter 45 which in turn displays the distance the drilling tool is raised from the bottom of the borehole. As long as the drilling tool remains elevated from the bottom of the borehole any downward movement from that position results in the down pulse train being passed to the counter 45 since the relay 44 is in its second operative state. The counter 45 subtracts from the up" count the down pulses which it receives until its count is returned to zero. Accordingly, the visual output of the counter 45 indicates the net distance between the drilling tool and the bottom of the borehole as the tool is lowered until the count is reduced to zero when the drilling tool contacts the bottom of the borehole. When the zero count is thus reestablished the counter 45 again provides the zero" signal to the relay driving amplifier 47 which in turn energizes the relay 44 to its first operative state. The down pulses occurring thereafter are permitted to pass to the counter 46.

It can be seen that the relay 44 operates essentially as an inhibiting device inhibiting the summing performed by the counter 46 when the display count of the counter 45 is greater than zero, and inhibiting the subtraction of the counter 45 when its count is not greater than zero. Any form of an inhibiting device capable of performing this function can be used in place of the relay 44, such as, for example, a solid-state or purely electronic inhibiting network.

As the borehole is deepened it is periodically necessary to add additional lengths of drill pipe to the drill string. When this is done the drill string is raised until the bottom of the kelly clears the rotary, the weight of the drill string is then supported independently of the traveling block by applying a slip so that the drill string is supported by the rotary 20, the kelly is removed, the additional length of drill pipe is added, the kelly is reinstalled above it, and the weight of the drill string is again applied to the traveling block 13. At the moment the weight of the drill string is first removed from the traveling block 13, after the drill string is raised, the hydraulic pressure in the conduit 42 drops below the calibration set-point of the pressure switch 40, which opens its contacts thereby preventing any further signals from the pulse generator 35 to pass to the discriminator 43. The displayed outputs of the counters, 45 and 46, remain unchanged as the traveling block is moved up and down to add the additional section of drill pipe. Thus the counter 46 indicates the total borehole depth while the counter 45 remains unchanged indicating the distance the drilling tool has been raised from the bottom of the borehole.

When the weight of the drill string is again applied to the traveling block, the pressure switch 40 closes its contacts and permits the system to respond to further signals generated by the pulse generator 35. Accordingly, the counter 45 indicates how far it must be further lowered from its raised position to contact the bottom of the borehole. This is a useful indication to prevent damage of the drilling tool as it is lowered.

During drilling operations there is always a portion of the weight of the drill string which is permitted to be applied to the drilling tool. Since the weight of the traveling block 13 is applied to the drilling cable both during the drilling operation, and during the addition of sections of drill pipe, the set-point of the pressure switch 40 is chosen to be at a value that corresponds to a supported load smaller than the supported portion of the drill string weight, and greater than the weight of the additional section of drill pipe added, both of these values being exclusive of the weight of the traveling block 13.

When casing is added to the borehole the entire drill string is raised and the drilling tool removed. When the tool is thus brought to the surface both counters 45, 46 display a count corresponding to the total depth of the borehole. As casing is lowered the counter 45 will subtract downwardly since the weight of the casing exceeds the set-point of the pressure switch 40. Hence, after the casing operation is completed the display signal of the counter 45 will be somewhere near zero even though the drilling tool is still on the surface. To prevent erroneous indications when the drilling tool is reinserted into the borehole the counter 45 is manually preset to a display indication equal to the depth of the borehole the moment that the drilling tool is reinserted at the surface.

It can be appreciated by those skilled in the art that any packaging arrangement can be used for the electronics, thus, for example, the discriminator 43 can be included within the counter assembly 45. Also, the components 40 through 47 can be mounted anywhere in the drilling structure. It is preferred that these components be mounted in the lower section so that the counters can be easily observed by the crew and a single electrical harness be used to carry the signals from the pulse generator 35 down to the pressure switch 40, and a short conduit 42 be used for coupling the pressure switch 40 with the force transducer 41, at the anchor point 25.

Referring now to FIG. 3 which is a cross-sectional view of FIG. 2 taken along the plane 33 the friction driven wheel 30 appears in end view and is shown engaging the sheave 28. Also appearing in end view is the mounting bracket 31 clamped to the flange of the [beam 32 with bolts 33.

Referring now to FIG. 4 which is an isometric view of the mounting bracket with the friction driven wheel 30 and the pulse generator 35, assembled thereto, the left portion of the mounting bracket 31 includes a channeled flange 50, having two threaded holes for the bolts 33, for clamping to the lower flange of the l-beam 32. Welded to the far end of the bracket 31 is a lower plate 51 having four threaded holes accepting bolts 52. An upper plate 53 is provided, for clamping a leafspring 54, to the lower plate 51. The leaf-spring 54 extends from the mounting bracket 31 in approximate perpendicular relationship therewith. Clamped to the end of the leaf-spring 54. is a yoke 55, which is clamped to the spring by a plate 56 which includes four threaded holes for accepting four bolts 57, passing through corresponding clearance holes in the yoke 55. In this manner the leaf-spring 54 is sandwiched between the yoke 55 and the plate 56. A pair of pillow block bearings are provided 58, 59 which are mounted on the upper surface of the arms of the yoke 55. The shaft of the friction driven wheel 30 is fitted to run in the pillow block bearings 58, 59 so that it can rotate freely within the arms of the yoke 55. Welded to the far arm of the yoke 55 is a right-angle bracket 60 to which is mounted the rotary pulse generator 35 in axially alignment with the friction driven wheel 30. A conventional mounting is used for the pulse generator employing three machine screws 61. A flexible drive coupling 65 is provided for coupling the shaft of the pulse generator 35 with the shaft of the driven wheel 30. A flexible coupling is preferred to protect the pulse generator 35 from radial or axial loading of its shaft from the driven wheel 30. FIG. 5 illustrates the coupling joining the two shafts.

The assembly of FIG. 4 is clamped to the lower flange of the l-beam 32 in a position such that the leaf-spring 54 is deflected through a distance sufficient to cause a driving load of about 40 pounds between the friction driven wheel 30 and the sheave 28. This configuration results in smooth and reliable operation of the pulse generator without slippage and with good repeatability.

While the invention has been described with a certain degree of particularity. it can, nevertheless, be seen by the descriptions hereinabove set forth, that many modifications and variations of the invention can be made without departing from the spirit and scope thereof.

Iclaim:

1. In a facility for drilling a borehole in the earth including a drilling structure positioned above a drill site, means including a drillstring coupled with a drilling tool for drilling said borehole, said structure including means for rotating set drillstring, first support means including a drilling cable for supporting said drillstring, a crown block having at least one rotatable sheave wherein said first support means is adapted to support a predetermined portion of the weight of said drillstring while said borehole is being drilled and wherein means are provided for interrupting the rotation of said drillstring and for supporting the weight of said drillstring independently of said first support means while at least one length of drill pipe is added to said drillstring by being hoisted to position for coupling thereto by said drilling cable, the predetermined portion of the weight of said drillstring being again supported by said first support means upon completion of the addition of said drill pipe, a system for providing first and second output signals representative, respectively, of the depth of said borehole and of the distance between said drilling tool and the bottom of said borehole comprising: a driven wheel rotatably mounted in said drilling structure in a position engaging said sheave for concurrent rotation therewith in association with the movement of said drilling cable; a bidirectional rotary pulse generator having an input shaft coupled with said driven wheel for proportional rotation therewith, said bidirectional pulse generator being adapted to provide a pair of electrical pulse train signals, the phase relationship between said pulse train signals representing the direction of rotation of said driven wheel thereby representing the direction of movement of said drillstring and each pulse of said pulse train signals representing the movement of said drillstring through an incremental length segment of predetermined magnitude; a discriminator electrically coupled with said pulse generator for discriminating between the phase of said pair of pulse train signals, said discriminator being adapted to provide first and second pulse train signals, the first pulse train signals corresponding to downward movement of said drillstring and the second pulse train signals corresponding to upward movement of said drillstring, each pulse of said first and second pulse train signals representing movement of said drillstring through an incremental length of predetermined magnitude; a first pulse counter electrically coupled with said discriminator for counting said pulses of said first pulse train signals and for providing a first output signal corresponding to the sum of said pulses of said first signals whereby said first output signal indicates the depth of said borehole in multiples of said predetermined incremental length segments as the distance said drillstring descends in said borehole; a bidirectional second pulse counter electrically coupled with said discriminator for counting said pulses of said second pulse train signals, said bidirectional pulse counter including subtraction means for subtracting from the resulting count of said second pulse train signals said pulses of said first pulse train signal thereby providing a second output signal corresponding to the resulting difference count whereby said second output signal represents the distance between said drilling tool and the bottom of said borehole, said second pulse counter being further adapted to provide an electrical third signal designating when its count is greater than zero and no signal when its count is not greater than zero; a relay electrically interposed between said discriminator and said first and second pulse counters for controlling the passage of said incremental depth first signal to said first and second counters, said relay being adapted to respond to said third signal by interrupting passage of said incremental depth of first signal to said first pulse counter when said count of said second pulse counter is greater than zero and by interrupting passage of said first signal to said second pulse counter when said count thereof is not greater than zero; a force transducer operatively coupled with said first support means for sensing the weight supported thereby and for providing a fourth signal representative thereof; and a switch operatively coupled with said force transducer and electrically interposed between said pulse generator and said first and second pulse counters, said switch being adapted to respond to said fourth signal by interrupting passage of said pulse train signal to said first and second pulse counters when said fourth signal indicates that the weight supported by said first support means is below a predetermined value which exclusive of the weight of said first support means is less than said predetermined supported portion of said drillstring weight and greater than the weight of said hoisted additional length of drill pipe whereby the movement of said drilling cable occurring during said addition of drill pipe is caused not to influence said first and second output signals of said first and second pulse coun- 

1. In a facility for drilling a borehole in the earth including a drilling structure positioned above a drill site, means including a drillstring coupled with a drilling tool for drilling said borehole, said structure including means for rotating set drillstring, first support means including a drilling cable for supporting said drillstring, a crown block having at least one rotatable sheave wherein said first support means is adapted to support a predetermined portion of the weight of said drillstring while said borehole is being drilled and wherein means are provided for interrupting the rotation of said drillstring and for supporting the weight of said drillstring independently of said first support means while at least one length of drill pipe is added to said drillstring by being hoisted to position for coupling thereto by said drilling cable, the predetermined portion of the weight of said drillstring being again supported by said first support means upon completion of the addition of said drill pipe, a system for providing first and second output signals representative, respectively, of the depth of said borehole and of the distance between said drilling tool and the bottom of said borehole comprising: a driven wheel rotatably mounted in said drilling structure in a position engaging said sheave for concurrent rotation therewith in association with the movement of said drilling cable; a bidirectional rotary pulse generator having an input shaft coupled with said driven wheel for proportional rotation therewith, said bidirectional pulse generator being adapted to provide a pair of electrical pulse train signals, the phase relationship between said pulse train signals representing the direction of rotation of said driven wheel thereby representing the direction of movement of said drillstring and each pulse of said pulse train signals representing the movement of said drillstring through an incremental length segment of predetermined magnitude; a discriminator electrically coupled with said pulse generator for discriminating between the phase of said pair of pulse train signals, said discriminator being adapted to provide first and second pulse train signals, the first pulse Train signals corresponding to downward movement of said drillstring and the second pulse train signals corresponding to upward movement of said drillstring, each pulse of said first and second pulse train signals representing movement of said drillstring through an incremental length of predetermined magnitude; a first pulse counter electrically coupled with said discriminator for counting said pulses of said first pulse train signals and for providing a first output signal corresponding to the sum of said pulses of said first signals whereby said first output signal indicates the depth of said borehole in multiples of said predetermined incremental length segments as the distance said drillstring descends in said borehole; a bidirectional second pulse counter electrically coupled with said discriminator for counting said pulses of said second pulse train signals, said bidirectional pulse counter including subtraction means for subtracting from the resulting count of said second pulse train signals said pulses of said first pulse train signal thereby providing a second output signal corresponding to the resulting difference count whereby said second output signal represents the distance between said drilling tool and the bottom of said borehole, said second pulse counter being further adapted to provide an electrical third signal designating when its count is greater than zero and no signal when its count is not greater than zero; a relay electrically interposed between said discriminator and said first and second pulse counters for controlling the passage of said incremental depth first signal to said first and second counters, said relay being adapted to respond to said third signal by interrupting passage of said incremental depth of first signal to said first pulse counter when said count of said second pulse counter is greater than zero and by interrupting passage of said first signal to said second pulse counter when said count thereof is not greater than zero; a force transducer operatively coupled with said first support means for sensing the weight supported thereby and for providing a fourth signal representative thereof; and a switch operatively coupled with said force transducer and electrically interposed between said pulse generator and said first and second pulse counters, said switch being adapted to respond to said fourth signal by interrupting passage of said pulse train signal to said first and second pulse counters when said fourth signal indicates that the weight supported by said first support means is below a predetermined value which exclusive of the weight of said first support means is less than said predetermined supported portion of said drillstring weight and greater than the weight of said hoisted additional length of drill pipe whereby the movement of said drilling cable occurring during said addition of drill pipe is caused not to influence said first and second output signals of said first and second pulse counters. 